7.2.1 Principles of IR Spectroscopy

• What is infrared (IR) spectroscopy used for?

  Identify functional groups
• IR spectroscopy is based on the ability of molecules to absorb specific frequencies of infrared radiation
• The O-H (Alcohol) functional group absorbs in the range of 3200-3600 $cm^{ - 1}$.
• What are the wavelength boundaries of the IR region in the electromagnetic spectrum?

  700 nm - 1 mm
• Molecules can vibrate in two primary ways: stretching and bending
• Each type of bond in a molecule has unique vibrational frequencies.
• What is the frequency range of the IR region in the electromagnetic spectrum?

  300 GHz - 400 THz
• IR spectroscopy helps identify functional groups by analyzing molecular vibrations
• What is the wavelength range of microwaves in the electromagnetic spectrum?

  1 mm - 30 cm
• Stretching vibrations involve the lengthening or shortening of chemical bonds along the bond axis.
• What does infrared (IR) spectroscopy identify in a compound?

  Functional groups
• Infrared (IR) spectroscopy identifies functional groups based on their characteristic absorption frequencies
• Different functional groups absorb IR radiation at the same frequencies.

  False
• Match the functional group with its characteristic absorption range in cm^{ - 1}</latex>:

  O-H (Alcohol) ↔️ 3200-3600

  C=O (Carbonyl) ↔️ 1650-1750

  N-H (Amine) ↔️ 3300-3500
• Arrange the steps in interpreting an IR spectrum:

  1️⃣ Identify characteristic peaks

  2️⃣ Determine wavenumbers

  3️⃣ Analyze peak intensities

  4️⃣ Assign peaks to functional groups
• What does wavenumber measure in an IR spectrum?

  Radiation frequency
• The O-H bond in alcohol produces a broad peak in the IR spectrum.
• The C=O bond in a carbonyl group produces a strong peak in the IR spectrum at approximately 1650-1750 $cm^{ - 1}$.Strong